Marc Brunel, an engineer from France, invents a method that allows workers to tunnel beneath rivers without water and mud. His “tunnel shield”, a rectangular, cast iron wall with many shutters, was made of dozens. Workers removed a few inches of dirt by opening the shutters one by one. Next, the entire shield was moved forward by screw jacks. The shield continued to move forward inches at a moment, and workers behind it built a thick brick lining, which became the tunnel’s shell. Brunel, who was the first to build an underwater tunnel 1,200 feet below London’s Thames River, was knighted after he completed the project.
The tunnel shield was modified to create many of the most impressive underwater passageways in the 20th Century, including the Lincoln and Holland tunnels in New York. Engineers installed an airtight seal system to counter the extreme pressure that was created by the tunnels’ construction, which caused flooding and structural collapses. Many workers spent their days compressing and decompressing. Although many workers suffered from decompression sicknesses, safety overall was much improved.
The Ted Williams Tunnel connects South Boston and Logan Airport. It is an example of the modern method for underwater tunneling-the immersed tub. Workers first dug a 50-foot trench on the Boston Harbor floor. Twelve massive steel tubes measuring 325 feet in length and already containing roads were then dropped into the water. After the tubes were connected to the harbor floor, the tunnels were buried under a protective 5-foot layer of rock. Workers finally removed the steel bulkheads from the tunnel and connected them to the roads. (For more information about the Ted Williams Tunnel, which is part of the 15 years Central Artery/Tunnel Project, please see “The Big Dig,” June 2001.
